This invention relates in general to radio receivers and more particularly to integrated digital radio receiver subsystems.
It is well known in the art that a dual conversion radio receiver converts incoming radio frequency (RF) signals using a common heterodyning process with two mixers. The RF signal is most often detected, converted and amplified into an audible format using some type of transducer such as a speaker. As seen in prior art FIG. 1, a known integrated radio receiver back-end or second intermediate frequency stage 10 will include an IF signal input 11 that is amplified by preamp 13 and then fed to a mixer 15 where it is mixed with a signal from a local oscillator synthesizer 17 controlled by a clock synthesizer 19. The resultant second IF signal is then processed by a bandpass sigma-delta (xcexa3-xcex94) converter 21 where it is noise shaped and converted into a digital format. Undesired out of band components of the converter signal can then be filtered using a discrete time filter 23. Thereafter, it is further processed and mixed to baseband using a frequency translator 25. Undesired components of this resultant signal are filtered using another discrete time filter 29 whose output is fed to the parallel to serial data converter 33 and the output 35. In order to limit the input signal to the xcexa3-xcex94 converter 21, an automatic gain control (AGC) circuit is employed to keep the xcexa3-xcex94 converter out of xe2x80x9cclipxe2x80x9d and reduce signal distortion.
Thus, as can be readily seen from FIG. 1, the radio receivers of today have greatly increased in complexity where they are not only highly integrated but also convert analog signals into a digital format where they can be manipulated and/or digitally processed for use as either audible information or data.
One problem typically associated of such high level integration of digital radio receiver has been to provide the back-end i.e. the second intermediate frequency (IF) components in addition to the digital mode sigma-delta converter in one integrated package. Specific obstacles such as analog or lumped filters (such as inductor-capacitor (LC) filters or ceramic resonators), have made such integrated circuits difficult to use and implement. Thus, the need exists to provide a highly integrated digital/analog RF receiver back-end which incorporates integrated filtering and a smart gain control that is easy to use with other receiver systems and offers superior performance characteristics.